Overhead gantry cranes and pilot gantry cranes are known for use in material handling, especially where high load conditions exist. Such pilot gantry crane typically utilize a rope or cable hoisting mechanism.
In the control procedures currently used for damping the load sway in cases where the rope length may change during the lifting operation, several damping control parameters have to be trimmed during use. An example of such a control procedure is described in "Pole-Placement Control of a Pilot Gantry" by Arto Marttinen, Proceedings of the 1989 American Control Conference, Jun. 21-23, 1989, Vol. 3, pp. 2824-2826. This trimming requires a large amount of computation. In addition, the trimming procedures currently used for damping the load sway require a precise determination of the position of the load. For this reason, in the currently used procedures a detector for measuring the load position must be placed on the load in many cases. Alternatively, U.S. Pat. No. 3,517,830 to Virkkala issued Jun. 30, 1970 uses a simplified sway damping arrangement in which the rope length is maintained "constant" during load movement.